Transport chains are used in industry to move objects from one place to another, for example in a factory. A transport chain can be constructed from a plurality of links that are similar in appearance and function and that are connected with one another. The connections between the links make it possible for the links to pivot relative to one another around two perpendicular axes of rotation which each extend with respect to the transport path's transport direction.
U.S. Pat. No. 4,597,492 describes a transport chain that consists of a plurality of identical plastic links interconnected by means of a joint segment. The joint segment has the form of a so-called Cardan joint with a steel pin that permits a vertical slewing motion, and a plastic plunge that permits lateral motion, which are mutually perpendicular and which extend in a transverse direction with respect to extension of the transport chain. The plastic links comprise a plate for carrying goods on their upper part, the underside of which constitutes a sliding surface that cooperates with the sliding surface of a conveyor beam's sliding surfaces. The body of the plastic link also has two protruding branches, which comprise holes in their central portion into which the steel pin is inserted, and which at their outer portion constitute engagement means for gear wheels on propulsion of the transport chain. This construction has a complicated structure and because of its Cardan joint results in a wide construction and thereby limits the size of the goods-carrying sliding surface against a sliding list. Another disadvantage is that the Cardan joint is not self-adjusting with respect to the main bearing that is constituted by the sliding surfaces between the goods-carrying plate's underside and the sliding list integrated into the conveyor beam.
U.S. Pat. No. 6,364,094 concerns a transport chain that consists of a plurality of identical plastic links interconnected by means of a joint segment, constructed according to the so-called ball coupling principle. Such a joint segment is constituted by a bearing element, namely a ball, and a pin centrally fixed to the ball. The pin is torsionally rigid with respect to the ball and the plastic link. The ball and the pin thereby form a fixed unit with respect to the plastic link, which fixed unit forms a pivot centre for the following plastic link. Turning motion is transmitted only via the ball. The pin's task is only to fix the ball and make it torsionally rigid.
The disadvantage of a centrally fixed pin in the ball is that the transmission of force from the ball to the following link is strongly concentrated at the nose section of the link and the ball, i.e. that part of the ball that lies at the front in the transport direction. A further disadvantage is that large demands are placed on the pin being so fixedly anchored that relative movement with respect to the ball, both radial and axial, cannot occur. This means that the pin requires both a large mounting force and also, during maintenance and repair work, a large disassembling force. Often, the special tools that are required for such mounting and disassembling work are not available at client locations where the conveyors are installed. Another disadvantage is that mounting and demounting of the ball is difficult so this is usually carried out from the side of the link and results in the formation of an opening that is larger than the diameter of the ball, which weakens the tensile strength of the construction.
The abstract of the Swedish patent no. SE 511 811 describes a plastic chain constructed according to the ball coupling principle and which comprises a ball and a pin that are manufactured as a single element from steel. The disadvantages of an integrated ball and pin are that such a component is expensive to manufacture, the wear between the steel ball and the following plastic link is relatively high and the force concentration from the ball to the following link is strongly concentrated at the nose sections of the link and the ball when the plastic chain is in use. The plastic material around the pin can therefore become deformed during use, which can create undesired play between the transport chain's components, which can in turn decrease the lifetime of the plastic chain and create noise.